Glow plug with permanent displacement resistant probe tip joint

ABSTRACT

A glow plug has a heater probe that can be axially misaligned relative to a central axis of an outer metal shell and of a center electrode and thereafter return automatically to its axially aligned configuration with the central axis. The outer shell has a through bore extending along the central axis. The center electrode is received in the though bore and extends along the central axis. The heater probe is attached in electrical communication with the center electrode in the through bore and extends along the central axis axially outwardly from a distal end of the shell. An annular flex joint provides the sole source of attachment of the outer shell to the heater probe via one end of the flex joint being attached to the outer shell adjacent the distal end and another end of the flex joint being attached to the heater probe.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 61/315,439, filed Mar. 19, 2010, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to glow plugs, and more particularly toceramic glow plugs.

2. Related Art

Ceramic glow plugs typically have an outer metal shell with a ceramicheater probe fixed partially therein. The heater probe extends axiallyoutwardly from the shell to a distal probe tip and axially into theshell to a proximal end configured for attachment to a center electrode.The heater probe is preferably maintained in coaxial alignment with acentral axis of the metal shell and the center electrode, such that thedistal probe tip extends into the cylinder bore in an intended locationto insure optimal ignition results. However, sometimes the heater probecan be plastically deformed by being bent out of axial alignment withcentral axis of the shell and center electrode, such as during assemblyor handling in general. When this occurs, the glow plug is generallyrendered inoperable.

SUMMARY OF THE INVENTION

A glow plug constructed in accordance with the invention has a heaterprobe that can be axially misaligned relative to a central axis of anouter shell and of a center electrode within the shell by an externallyapplied radial force, and thereafter return automatically substantiallyto its original axially aligned configuration with the central axis ofthe shell and center electrode upon removing the applied force withoutthe glow plug being damaged. The metal outer shell has a through boreextending along the central axis between a proximal end and a distalend. The center electrode is received in the though bore and extendsalong the central axis. The heater probe is attached in electricalcommunication with the center electrode in the through bore and extendsalong the central axis axially outwardly from the distal end of theshell. An annular flex joint provides the sole source of attachment ofthe outer shell to the heater probe. The flex joint has one end attachedto the outer shell adjacent the distal end and another end attached tothe heater probe. The flex joint has an annular leg extending radiallybetween the outer shell and the heater probe. As such, if an externalforce is applied to the probe tip along a generally lateral ortransverse direction to the central axis, the flex joint allows theheater probe to temporarily flex elastically out of axial alignment withthe outer shell and the center electrode, while automatically biasingthe heater probe back to, or substantially back to, its axially alignedposition relative to the shell and center electrode upon release of theexternally applied force. Accordingly, the glow plug can withstandinadvertent bending of the heater probe without becoming plasticallydeformed or otherwise damaged.

In accordance with another aspect of the invention, the flex joint has areverse folded portion extending axially between the outer shell andheater probe.

In accordance with another aspect of the invention, the flex joint has adouble, Z-shaped reverse folded portion extending axially between theouter shell and heater probe.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of the invention willbecome more readily appreciated when considered in connection with thefollowing detailed description of presently preferred embodiments andbest mode, appended claims and accompanying drawings, in which:

FIGS. 1A-1D illustrates a test to assess the ability of a glow plugheater probe to withstand a force applied laterally to the heater probetip;

FIG. 2 shows a glow plug constructed in accordance with one aspect ofthe invention; and

FIGS. 3A-3G show enlarged cross-sectional views of variousconfigurations of the area designated 3A-3G in FIG. 2 in accordance withthe invention.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

Referring in more detail to the drawings, FIG. 2 illustrates a glow plug10 constructed in accordance with one presently preferred embodiment ofthe invention. The glow plug 10 has an annular outer metal shell 12 withan inner surface 13 bounding a through bore 14 which extends along alongitudinal central axis 15 of the shell 12 between a proximal end 17and a distal end 19. The metal shell 12 may be formed from any suitablemetal, such as various grades of steel, and may also incorporate aplating or coating layer, such as a nickel or nickel alloy coating on anexterior, also referred to as outer surface 16, and the bore 14, toimprove the resistance of shell 12 to high temperature oxidation andcorrosion. The glow plug 10 also includes a heater assembly 18. Theheater assembly 18 has a heater probe 20 and a center electrode 22attached to the heater probe 20. In accordance with the invention, anannular flex joint as shown in various configurations in FIGS. 3A-3G,and indicated as 24 in FIG. 3A, fixes the heater probe 20 to the shell12. As shown in FIGS. 1B-1C, the flex joint 24 allows the heater probe20 to temporarily flex elastically out of axial alignment with thelongitudinal axis 15 relative to the outer shell 12 and the centerelectrode under an externally applied force (F) over a lateraldisplacement (D1), while automatically biasing the heater probe 20 backto, or substantially back to, its axially aligned position relative tothe shell 12 and center electrode 22 (FIG. 1D) such that any residualdisplacement (D2) is negated or negligible. Accordingly, the heaterprobe 20, upon being bent out of axial alignment from the longitudinalaxis 15 can return automatically back to axial alignment with the axis15, and thus, can withstand inadvertent bending without becomingpermanently or plastically deformed or otherwise damaged.

The flex joint 24 is preferably constructed of a material having arelatively low Young's modulus and high yield strength. In addition, thematerial preferably is selected having a thermal expansion coefficientclosely matched with the material of the heater probe 20, such as Kovar,Thermospan, Incoloy 903, Inconel 718 or the like, to allow directattachment of the flex joint 24 to the heater probe 20. The flex joint24 can be attached to the shell 12 by an interference fit, brazing, orwelding, for example, and to the heater probe 20 by brazing,particularly for ceramic probes, and by an interference fit, brazing orwelding, particularly for metal probes.

As shown in FIG. 3A, the flex joint 24 extends between opposite freeends 26, 28, wherein one free end 26 extends radially outwardly from theaxis 15 and is attached directly to the inner surface 13 of the shell 12in a butt joint immediately adjacent the free distal end 19 of the shell12. The free end 19 is shown having an annular chamfered surface, alsoreferred to as nose 42, that extends obliquely to the central axis 15generally toward the proximal end 17 of the shell 12 to, orsubstantially to the outer surface 16 of the shell. The flex joint 24has a single reverse fold 30, with an annular leg 32 extending axiallyand generally parallel with the axis 15 from the free end 26 toward thecenter electrode 22 to the reverse fold 30 and another annular leg, alsoreferred to as an annular collar 34, extending axially and generallyparallel with the axis 15 from the reverse fold 30 toward a free end ortip 36 of the heater probe 20. As such, the leg 32 extends axiallybetween the shell 12 and the collar 34 in detached relation therefromwith an annular gap or space 37 being formed between the leg 32 andshell 12 and an annular space being formed between the leg 32 and collar34. The collar 34 has an inner, radially inwardly facing annular surface38 that is attached to an outer surface 40 of the heater probe 20. Thebond is formed via one of the mechanisms discussed above and extendssubstantially along the length of the collar 34, wherein the collar 34extends from the reverse fold 30 within the through bore 14 of the shell12 axially outwardly of the shell 12. In the embodiment illustrated, byway of example and without limitation, about ½ the length of the collar34 is received in the through bore 14 and about ½ the length extendsaxially outwardly from the through bore 14.

As such, when an external force is applied to the heater probe 20, suchas shown in FIGS. 1A-1D, the heater probe 20 is able to flex laterallyrelative to the axis 15 in an elastic mode of deformation such that theheater probe 20 is able to return automatically to, or substantially toits original non-flexed position in coaxial alignment with the axis 15.Preferably, the distance of lateral displacement permitted by the flexjoint 24 without encountering permanent or plastic deformation of theheater probe 20 relative to the axis 15 is about 1.5 mm. The relativelyhigh degree of elastic deformation is provided by the areas of the flexjoint 24 that are free and unattached from the heater probe 20 and shell12, with particular regard to the leg 32.

Another flex joint 124 constructed in accordance with the invention isshown in FIG. 3B, wherein similar reference numerals, offset by a factorof 100, are used to identify like features as discussed above. The flexjoint 124 extends between opposite free ends 126, 128, wherein one freeend 126 extends radially outwardly from the axis 115 and is everted overa chamfered nose 142 of a shell 112 with a surface 44 immediatelyadjacent the free end 126 being attached in bonded relation directly tothe chamfered nose 142 and extending flush with or substantially flushwith an outer surface 116 of the shell 112. The flex joint 124 has asingle reverse fold 130, with a pair of an annular legs 132, 132′extending generally axially and generally parallel to one another,although in a slight angular relation with the axis 115, from thereverse fold 130 toward a tip 136 of the heater probe 120. The leg 132′transitions to a cylindrical collar 134 adjacent the nose 142, whereinthe collar 134 is attached to an outer surface 140 of the heater probeas discussed above with regard to the collar 34. As such, the legs 132,132′ extend generally axially between the shell 112 and the heater probe120 in detached relation therefrom with a pair of annular gaps or spaces137, 137′ being formed between the legs 132, 132′ and shell 112 andheater probe 120, respectively, and an annular space 139 being formedbetween the legs 132, 132′, wherein the spaces 137, 137′, 139 areradially aligned with one another. The collar 134 has an inner, radiallyinwardly facing surface 138 that is attached to the outer surface 140 ofthe heater probe 120. The bond is formed via one of the mechanismsdiscussed above and extends substantially along the length of the collar134, wherein the collar 134 extends from adjacent the nose 142 axiallyaway from the shell 112.

Another flex joint 224 constructed in accordance with the invention isshown in FIG. 3C, wherein similar reference numerals, offset by a factorof 200, are used to identify like features as discussed above. The flexjoint 224 is similar the flex joint 124, however, rather than having alip everted over a nose of a shell 212, a surface 244 adjacent a freeend 226 is attached to an inner surface 213 of the shell 212 adjacentthe nose 242, with the free end 226 shown being flush with the nose 213,by way of example and without limitation. Otherwise, the flex joint 224is the same as the flex joint 124, including having a single reversefold 230, with a pair of an annular legs 232, 232′ extending generallyaxially in generally parallel relation with one another, although in aslight angular relation with the axis 215, from the reverse fold 230toward a tip 236 of the heater probe 220. The leg 232′ transitions to acylindrical collar 234, wherein the collar 134 is attached to an outersurface 240 of the heater probe 220. A pair of annular gaps or spaces237, 237′ are formed between the legs 232, 232′ and shell 212 and heaterprobe 220, respectively, and an annular space 239 is formed between thelegs 232, 232′. A radially inwardly facing surface 238 of the collar 234is attached to the outer surface 240 of the heater probe 220, whereinthe bond is formed via one of the mechanisms discussed above.

Another flex joint 324 constructed in accordance with the invention isshown in FIG. 3D, wherein similar reference numerals, offset by a factorof 300, are used to identify like features as discussed above. The flexjoint 324 is similar the flex joint 24 of FIG. 3A, however, rather thanhaving a free end 326 attached to an inner surface 313 of a shell 312, aradially outward facing surface 344 of a radially outer first leg, alsoreferred to as outer collar 334′, is attached to the inner surface 313of the shell 312, while a radially inner second leg, also referred to asinner collar 334, is attached to an outer surface 340 of the heaterprobe 320 as discussed above for FIG. 3A. The outer collar 334′ andinner collar 334 are attached along their full length to the respectiveinner surface 313 and outer surface 340. Rather than having a singlereverse fold as in the previous embodiments, the outer collar 334′provides the flex joint 324 with a pair of reverse folds 330, 330′ withan annular third leg 332 extending axially and generally parallel withthe axis 315. The third leg 332 extends axially between the outer collar334′ and the inner collar 334 in detached, radially spaced relationtherefrom. An annular gap or space 337 is formed between the leg 332 andouter collar 334′ and an annular space 339 is formed between the leg 332and the inner collar 334. Accordingly, the leg 332 and outer collar 334′are spaced radially from one another and the leg 332 and the innercollar 334 are spaced radially from one another. The collars 334′, 334and third leg 332 are in radially aligned configuration with one anotherforming a generally Z-shaped wall in axial cross-section such that thegaps 337, 339 are also radially aligned with one another. The innercollar 334 is attached to the heater probe 320 as discussed above withregard to FIG. 3A.

Another flex joint 424 constructed in accordance with the invention isshown in FIG. 3E, wherein similar reference numerals, offset by a factorof 400, are used to identify like features as discussed above. The flexjoint 424 is similar the flex joint 324 of FIG. 3D, however, rather thanhaving the full length of an outer first leg, also referred to as outercollar 434′, attached to an inner surface 413 of a shell 412, only aportion of the outer collar 434′ immediately adjacent a free end 426 isattached to the inner surface 413, while a portion of the outer collar434′ adjacent a reverse fold 430′ located adjacent and radially inwardlyfrom a nose 442 remains detached radially inward from the inner surface413 of the shell 412. Likewise, rather than having the full length of aninner second leg, also referred to as inner collar 434, attached to anouter surface 440 of a heater probe 420, only a portion of the innercollar 434 immediately adjacent a free end 428 is attached to the outersurface 440, while a portion of the inner collar 434 adjacent a reversefold 430 located between the shell 412 and the heater probe 420 remainsdetached from the outer surface 440 of the heater probe 420. The outercollar 434′ provides the flex joint 424 with a pair of reverse folds430, 430′ with an annular third leg 432 extending axially and generallyparallel, though slightly angled with respect to an axis 415. The thirdleg 432 extends axially between the outer collar 434′ and the innercollar 434 in detached relation therefrom. An annular gap or space 437is formed between the third leg 432 and outer collar 434′ and an annularspace 439 is formed between the third leg 432 and the inner collar 434.The collars 434′, 434 and third leg 432 are in radially alignedconfiguration with one another forming a generally Z-shaped wall inaxial cross-section such that the gaps 437, 439 are also radiallyaligned with one another.

Another flex joint 524 constructed in accordance with the invention isshown in FIG. 3F, wherein similar reference numerals, offset by a factorof 500, are used to identify like features as discussed above. The flexjoint 524 has similarities to the flex joint 24 of FIG. 1, in that itextends between opposite free ends 526, 528, wherein one free end 526extends radially outwardly from an axis 515 and is attached directly toan inner surface 513 of the shell 512 in a butt joint. However, ratherthan having a reverse fold, a leg 532 extends radially inwardlygenerally transverse to the axis 515 and transitions directly to acylindrical leg portion, also referred to as collar 534. The collar 534extends axially outwardly from a distal end 519 of the shell 512 towarda tip 536 of the heater probe 520 and is fixed along its full axiallyextending length to an outer surface 540 of the heater probe 520 asdiscussed above with regard to the collar 34 of FIG. 3A. As such, ratherthan a reverse folded leg providing the flex joint 524 with it abilityto flex angularly relative to the axis 515, it is the radially extendingannular leg 532 that provides the freedom to flex. Accordingly, thedegree of elastic flex can be regulated by controlling the length of theleg 532, with the flex increasing and decreasing as the length isincreased and decreased, respectively.

Another flex joint 624 constructed in accordance with the invention isshown in FIG. 3G, wherein similar reference numerals, offset by a factorof 600, are used to identify like features as discussed above. The flexjoint 624 is similar to the flex joint 524, having opposite free ends626, 628, wherein one free end 626 extends radially outwardly from anaxis 615 and is attached directly to an inner surface 613 of the shell612 in a butt joint. Further, a leg 632 extends radially inwardlygenerally transverse to the axis 515 and transitions directly to acylindrical second end, also referred to as collar 634. The collar 634extends axially toward a tip 636 of the heater probe 620 and is fixed toan outer surface 640 of the heater probe 620 via one of the mechanismsdiscussed above with regard to the collar 34 of FIG. 3A. However, ratherthan the entire length of the collar 634 being attached to the heaterprobe 620, as with the collar 534 discussed above, only a distal portionof the collar 634 immediately adjacent the free end 628 is attached tothe heater probe 620. An axially proximal portion of the collar 634immediately adjacent the leg 632 remains spaced radially from anddetached from the heater probe 620, with an annular space 637′preferably being formed between the collar 634 and the heater probe 620.Accordingly, an increase degree of angular elastic deflection isprovided by the gap 637′.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

1. A glow plug, comprising: a metal outer shell having a through boreextending along a central axis between a proximal end and a distal end;a center electrode received in said though bore and extending along saidcentral axis; a heater probe attached in electrical communication withsaid center electrode in said through bore and extending along saidcentral axis axially outwardly from said distal end of said shell; andan annular flex joint providing the sole source of attachment of saidouter shell to said heater probe, said flex joint having one endattached to said outer shell adjacent said distal end and another endattached to the said heater probe, said flex joint having an annular legextending radially between said outer shell and said heater probe. 2.The glow plug of claim 1 wherein said leg has at least one portionextending substantially parallel to said central axis in radially spacedrelation with said shell and said heater probe.
 3. The glow plug ofclaim 2 wherein said leg has at least a pair of portions extendingsubstantially parallel to one another between said shell and said heaterprobe.
 4. The glow plug of claim 3 wherein said leg is generallyZ-shaped.
 5. The glow plug of claim 4 wherein a first portion of saidZ-shaped leg is fixed to said shell, a second portion of said Z-shapedleg is fixed to said heater probe, and a third portion extend betweensaid first portion and said second portion with a radial clearanceformed between said first, second and third portions.
 6. The glow plugof claim 5 wherein a portion of said first portion is detached inradially spaced relation from said shell.
 7. The glow plug of claim 6wherein a portion of said second portion is detached in radially spacedrelation from said heater probe.
 8. The glow plug of claim 5 whereinsaid first portion is entirely attached to said shell.
 9. The glow plugof claim 8 wherein said second portion is entirely to said heater probe.10. The glow plug of claim 5 wherein said first, second and thirdportions are spaced radially from one another.
 11. The glow plug ofclaim 1 wherein said distal end of said shell has a chamfered noseextending toward an outer surface of said shell and said one end of saidflex joint being everted over said chamfered nose in bonded relationthereto.
 12. The glow plug of claim 1 wherein said annular legtransitions to a cylindrical portion extending axially outwardly fromsaid distal end of said shell.
 13. The glow plug of claim 1 wherein saidcylindrical portion is entirely fixed to said heater probe.
 14. The glowplug of claim 1 wherein said cylindrical portion has a portion spacedradially from said heater probe and a portion fixed to said heaterprobe.